A structural panel including a honeycomb core and a foamed polymer composition

ABSTRACT

The composite panel is comprised of three spaced skins. A foam synthetic polymer composition material is adhesively secured between the first and second skins, while a honeycomb is positioned between the second and third skins.

United States Patent Jamison et al. i Feb. 25, 1975 1 A STRUCTURAL PANELINCLUDING A HONEYCOMB CORE AND A FOAMED [56] References Cited POLYMERCOMPOSITION UNITED STATES PATENTS [75] inventors: John W. Jamison, CostaMesa; 3,000,144 9/1961 Kitson 52/309 Robert R. Black, Jr., Lehabre', Roy3,629,046 1/1971 Gilbert..... 161/161 X E Denney, placentia all of3,646,721 3/1972 Becker 52/618 3,656,992 4/1972 Lynam et a1 161/68 X 1Asslgneer Hughes Aircraft p y Culver 3,711,363 1/1973 .larema et a1,161/161 Clty, Cal1f. 3,732,138 5/1973 Almog 52/618 X [22] Filed: Feb.16, 1973 Primary Exammer-Phflrp D1er 1 1 PP 333,109 Attorney, Agent, orFirmAllen A. Dicke, Jr.; W. H.

Related U.S. Application Data MacAnster [62] Division of Ser. No.235,893, March 20, 1972,

abandoned. 1 1 ABSTRACT The composite panel is comprised of three spaced1 1 Cl 1/68, 52/309, 2/615, skins. A foam synthetic polymer compositionmaterial 5 1, 161/90 is adhesively secured between the first and second1 lllt- B321) E046 1332b skins, while a honeycomb is positioned betweenthe B32b 27/ second and third skins. [58] Field of Search 161/68-69,

5 Claims, 5 Drawing Figures A STRUCTURAL PANEL INCLUDING A HONEYCOMBCORE AND A FOAMED POLYMER COMPOSITION CROSS REFERENCE This applicationis a division of patent application Ser. No. 235,893, filed Mar. 20,1972, now abandoned by John W. Jamison, Roy E. Denner, and Robert R.Black, Jr. for Shelter Construction.

BACKGROUND This invention is directed to a composite structural panelhaving low thermal conductivity and improved mechanical strength.

Shelters of various sorts have been built since the earliest beings onearth evidenced intelligence. The particular shelters of this inventionare related to modern high performance concepts. Attention has beengiven to modular methods of containerization of equipment. While such isuseful in military circumstances, it is also useful for other,non-military ends, where equipment protection is desired, together withmobility. Such situation is found at construction sites, particularlysites of heavy construction, such as bridges, dams, highways, officebuildings, and in oilfield use. The advantage of the modular techniqueis the relative ease with which equipment enclosed in such a shelter canbe transported and deployed. As used with respect to this invention, theterm shelter refers to a special type of container which can be used tohouse equipment of electrical nature, or other types, and is largeenough so that the equipment enclosed can be operated by technicianswithout removing the equipment from a shelter. Additionally, the shelteris weatherproof construction, since it may be deployed under extremeenvironmental conditions. While the shelter is expected to permanentlyhouse equipment under such conditions, it should be noted that the termshelter is applied to the housing, rather than the combination and,furthermore, the shelter may be employed only to protect the equipmentduring transportation in cases where the equipment is subsequentlyunloaded.

Several manufacturers build shelters, and various panel constructionshave been employed, but none of the shelters or panel constructions havebeen as advantageous as those described with respect to this invention.Previous panel constructions of sandwich construction have been the mostsuccessful. This prior construction consists of two relatively thin,high density, high strength facings bonded on opposite sides of arelatively thick, low density, low strength core. The facings carry theload in the plane of the panel, while the core carries shear stressesand resist compression loads normal to the plane of the panel. Aluminumfacings of various thicknesses are generally employed. Paper honeycomb,polymer composition foam with or without reinforcement therein, plywood,and aluminum honeycomb have been used as core materials. However, eachof these by itself has disadvantages when all environmental, weight andloading problems are considered.

The principal shelter requirements which advise against the use of theabove-listed core materials are the requirement of being moisture-proof,having adequate thermal insulation, having capacity for random insertinstallations and the weight limits imposed upon the finished shelters.The paper honeycomb provides high strength-to-weight ratio, but itcannot meet the moisture-proof requirements. Polymer composition foamalone is a thermal insulator of adequate value, but it has inadequatestrength for random insert installation. Polymer composition foam withstrengthening beams lying on edge therein satisfies the thermal andstrength requirements, but is usually too heavy, is expensive toconstruct, and has no capacity for random insert installation. Plywoodalone is too heavy. An aluminum honeycomb core does not satisfy thethermal requirements.

Once a panel of adequate thermal and structural propertiies has beenachieved, it is also necessary to provide a means for joining two panelsand/or terminating a panel edge. To accomplish this, closeouts andjoints between panels must be provided. Flexible or semi-rigid jointscharacterize the shelter assemblies of the prior art, with cost and easeof assembly being cited as the primary reasons for the flexible joint.It has also been argued that a flexibly-joined structure will besubjected to lower acceleration levels during shock loading. However,the primary failure of shelters is the leakage of moisture. This leakageis often the result of joint failure which has resulted from panelmovement. The flexible joint construction used by several manufacturersconsists of a thin-walled extrusion tee, or channelangle combinationfastened in some manner to attach intersecting panels. Several of thistype, applicable to sandwich construction panels, are described in U.S.Pat. No. 2,986,245.

SUMMARY In order to aid in the understanding of this invention, it canbe stated in essentially summary form that it is directed to a shelterconstruction. The composite panel comprises first, second, and thirdskins with a foam synthetic polymer composition material secured betweenthe first and second skins and a honeycomb core attached between thesecond and third skins. According to one aspect of this invention, theshelter includes panels which are of composite construction includingtwo outer metallic sheet layers, an inner sheet layer, with a honeycomband a polymer composition layer between the sheet layers. The entirepanel is bonded together so that the panel provides a high strength, lowthermal conductivity and low weight panel for shelter construction. Inaccordance with another aspect of this invention, a panel has a polymerfoam core, with the surface thereof provided with scores into which theadhesive securing the skin to the foam layer is intruded, to increasepeel resistance. In accordance with yet another aspect of thisinvention, the shelter is built up of panels having inner and outerskins together with a core therebetween, together with a closeout bar onat least one panel edge. The closeout bar is adhesively secured betweenthe skins, adjacent the core, and is configured for rigid attachmentwith a similar closeout bar.

Accordingly, it is an object of this invention to provide a shelterconstruction which includes a multilayer panel of adequate strength andminimum thermal conductivity and minimum weight characteristics andcapacity for randomly-located insert installation using material whichare highly resistant to water penetration and water damage. It isanother object to provide such a panel in which a closeout bar ispositioned in the edge thereof for panel attachment. It is yet anotherobject to provide a closeout bar which is rigidly secured to the paneland can be rigidly secured to another closeout bar. It is yet anotherobject to provide a closeout bar of extruded shape to provide a uniformcross section. It is still another object to provide a panel ofmultilayer construction, including a polymer foam layer wherein the skinis adhesively attached to the polymer foam. It is a further object toprovide a scored surface on the polymer foam layer so that increasedadhesive engagement is achieved to increase peel strength. It is stillanother object to provide a multilayer panel including inner and outerskins, with both polymer foam and honeycomb between the skins thereof.Other objects and advantages of this invention will become apparent froma study of the following portion of the specification, the claims, andthe attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of ashelter having panels and corner joints, in accordance with thisinvention.

FIG. 2 is an enlarged partial section taken generally along the line 22of FIG. 1.

FIG. 3 is similar to FIG. 2, but showing such a joint secured withscrews rather than rivets.

FIG. 4 is an enlarged broken-out part of the panel construction, withparts broken away, to show the several layers.

FIG. 5 is an enlarged partial section taken generally along the line 5-5of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a shelteris illustrated therein. In the preferred utility of the shelterconstruction of this invention, the shelter 10 is of sufficient size tocontain and protect electronic equipment, and to permit the entry ofpersonnel therein for using the equipment. In military situations, theshelter may contain communication equipment and operators, or maycontain radar equipment, consoles and operators, and the like. Innon-military utilization, the shelter may contain field instrumentationand recording equipment, or it may contain record storage andutilization equipment and a computer input, as might be employed atheavy construction sites. Thus, in the preferred embodiment, the shelter10 is of such size as to permit the entry of personnel. To permit thisentry, door 12 is provided in end 14. Various other devices to permitthe utilization of the shelter by personnel can also be incorporated inthe shelter, such as interior lighting and ventilation devices.Illustrated with respect to shelter side 16 are ladder elements 18 topermit convenient access to the top'20 of the shelter. In accordancewith the preferred embodiment, the shelter 10 also has a far end, farside and bottom. Each of these six walls of the shelter is at leastsemi-permanently attached to the others to provide a complete, rigidstructure. The shelter is intended to be permanently assembled, withdisassembly of parts thereof only for special purposes; the shelter isnot intended to be disassemblable for transportation in its preferredutilization.

While this disclosure is directed to a shelter 10 which is of such sizeas to permit entry of personnel therein for the purpose of access toequipment in the shelter for its utilization or repair, it is clearthat, in accordance with the teachings of this invention, the structurethereof is equally useful for smaller enclosures, to protect theequipment enclosed therein from the environment.

The shelter construction of this invention comprises a panelconstruction which is useful with several types of corner joints, and acorner joint which is useful with several types of panel constructions.However, they are particularly useful with each other to define a panelhaving edges suitable for joining. Referring to FIG. 2, a portion of theend wall 14 is shown therein. The end wall 14 comprises a panel 22finished at its edge with closeout 24, which serves as a joining devicefor the end wall 14 and the other walls of the shelter. First discussingthe panel 22, each of the panels of the various walls is the same andcomprises an inner skin 26, honeycomb core 28, divider skin 30,synthetic polymer composition rigid foam core 32, and outer skin 34. As

. seen in FIGS. 2, 3, and 4, the honeycomb cells aresubstantially'normal to the skins, as in conventional structuralhoneycomb practice. In the preferred embodiment, inner skin 26,honeycomb 28, and divider facing 30 are of aluminum with a corrosionprotective finish. Usually, the divider skin 30 is thinner than theinner and outer skins, because it carries less of the load of thecomposite core panel 22. All elements the skins, foam core 32, honeycombcore 28, and divider skin 30 are adhesively secured together by means ofa sheettype adhesive cured at elevated temperature. The polymer foamcore in the preferred embodiment is preferably a rigid foam ofpolymethacrylimid, of 3 pounds per cubic foot density, which isconveniently secured by high strength epoxy adhesive.

In the preferred embodiment, the outer skin 34 is also aluminum sheet.Other suitable structural foams are formed from polyvinylchloride andpolyurethane. Other skin materials include plywood and synthetic polymercomposition sheets.

In order to obtain greater peel resistance of the bonding, anintersecting pattern of grooves 36 is cut on the side of foam core 32toward divider skin 30, and an intersecting pattern of grooves 38 is cuton the side of the foam core 32 toward outer skin 34. These groovesshould be cut to a depth of about half their lateral spacing as amaximum, and should be cut as narrow as possible consistent with theinflow of adhesive therein. Razor cuts are satisfactory, for theadhesive readily wets the surfaces. FIGS. 4 and 5 illustrate theadhesive layers 40 and 42, and FIG. 5 particularly shows the inflow ofthe adhesive into the grooves. When the adhesive identified above isemployed, a razor cut groove is preferred.

The employment of these grooves improves the peel resistance of theskins from the polymer foam core by increasing the tear area or shearline in the foam core as the skin is peeled away. For example, if outerskin 34 were peeled away from polymer foam core 32, failure would occurabout along the dotted lines 44 and 46 of FIG. 5.

As thus constructed, the panel construction provides thermal insulationcapability, in accordance with the characteristics of the polymer foam.The thickness, density, and thermal conductivity of the polymer foamlayer 32 can be selected so that an overall heat transfer coefficientconsistent with shelter requirements can be obtained without appreciablyaffecting the shelter weight or strength. Furthermore, in thisconstruction, potted insert fasteners can be inserted into the honeycombat random locations to transmit unit loads into the inner skin 26 anddividier skin 30. These inserts can be installed anywhere in thealuminum honeycomb core, and complete versatility exists as the numberand location thereof without need for additional secondary supportingstructure. Furthermore, the panel components are all highly insensitiveto water damage and degradation, when compared to other panels. Thehoneycomb core, together with its inner skin and divider skin providesthe strength and moisture resistant requirements of the shelterconstruction, so that balance results and optimum characteristics arerealized. In cases where adequate core strength can be provided bystructural foam, a two-skin structure with foam core is feasible.

FIG. 2 illustrates closeout 24 in the edge of panel 22, and closeout 48in the edge of side panel 16. Each of the walls of shelter is formed ofpanels, as previously descirbed, and each of the panels must have atransitional member at the panel edges. The closeouts illustrated arethe preferred panel construction, with the same closeout extendingaround all four peripheral edges of each panel. The closeouts aredesigned so that they cooperate with each other to seal, and can beemployed in any corner, as well as between panels edgewise oriented andlying generally in the same plane. However, other joints can be used inspecific locations, where desired. The particular corner jointconstruction illustrated in detail in FIGS. 2 and 3 need not necessarilybe employed with, or only with, the specific panel constructionillustrated in detail in FIGS. 4 and 5. With this understanding that thecloseout edge joint describedas being the preferred embodiment, but notnecessarily the exclusive embodiment of closeout for the panels, theillustrative embodiments thereof are described below.

Each of the closeouts 24 and 48, as well as the other bars, are ofidentical construction and are of uniform cross section so that they canbe extruded and used for corner joints or edgewise joining of panels.Closeout 24 is illustrative and will be described in detail. Closeout 24has walls 50 and 52 which are joined out by back web 54 and center web56. Skins 26 and 34, respectively, lie against walls 50 and 52 with theback web 54 against the core material of panel 22. The closeout 24 isplaced in position during the assembly of the panel and is adhesivelysecured between the skins when the entire panel is completed. It ispreferred that the back web 54 be adhesively secured to the corematerial at the same time. In addition, since it is adhesively securedto the skin and to the core, it is rigidly attached and is an integralpart of the panel.

The foreward end of the closeout includes a nose 58 which is defined byfront web 60 and center wall 62. Center wall 62, together with centerweb 64, defines a recess into which the nose 66 of closeout 48 extends.Nose 58 is, in effect, a square, the side dimensions of which are halfthe distance between the outside of the skins 26 and 34 so that therecess into which nose 66 extends is of the same dimension. Thus, aninterlocking nose and recess joint is provided.

In the case where panels are of different thickness, a correspondingnumber of closeout cross-sections are required. The material of thecloseout is any convenient extrudable material. Aluminum extrusionssupply some of the required properties. but where thermal conductivityis to be minimized, materials of lower thermal conductivity areemployed. For example, a fibreglass-epoxy extrusion is desirable forthis use. The strength is adequate, it is light of weight to minimizethe total shelter weight, and is convenient for fastening, whileproviding the low thermal conductivity desirable. Since the inner skinsof the two panels overlap, radio frequency interference andelectromagnetic interference protection is maintained for the equipmentwithin the shelter. If desired, an adhesive or paste containing an RFIand/or EMI conductive material can be applied at the juncture 68 tomaintain sealing integrity.

Securement is accomplished by means of drilling through the outer walls,as at holes 70 and 72, to permit drilling of rivet holes and theinstallation and upsetting of rivets 74 and 76. After the joint is thuscompleted, an external scuff seal 78 is adhesively attached. Since thescuff seal overlaps the outer skins of the adjacent panels, when thescuff seal is aluminum to match the skin material and RFl-EMI materialis included in the adhesive, additional sealing integrity is provided.

If it is desired that the joints between panels be conveniently laterdemountable, without the need for drilling out rivets such as rivets 74and 76, machine screws can be used as an alternative fastening betweenthe closeouts. Referring to FIG. 3, panels 80 and 82, identical topanels 22 and 16, have closeouts 84 and 86 identical to closeouts 24 and28. After the drilling for the fasteners, threaded inserts 90 and 92 areadhesively secured in holes for the reception of machine screws 94 and96.

In an alternative embodiment, the space between webs 56 and 64 could befull, or web 64 more heavy so adequate thread engagement thereineliminates the need for an insert, and the holes can be tapped directlyinto the web. A suitable RFI-EMI compound is inserted in ajoint at atime of securement but, in this case, it is preferably not in adhesivevehicle. After the shelter is assembled, it may be demounted by removalof the scuff seal 98, followed by removal of the machine screws at theseveral joints. It may be desired that every joint be demountable, sothat-the entire shelter can be disassembled. On the other hand, it maybe desirable that only one of the side wall panels be demountable sothat equipment access is achieved, either for maintenance of theequipment or for the installation and removal of larger pieces ofequipment.

The particular advantages of the joint include the fact that such ajoint provides a highly efficient structural joint (due to theconfiguration and fastener placement) which is weather-proof andmoisture resistant. Furthermore, the joint provides shielding againstradio frequency interference and electromagnetic interfer ence, betweenthe contents of the shelter and the exterior environment. It must alsobe noted that the corner joint does not have exposed rivets or otherfasteners due to the placement of the fasteners and the scuff seal. Theexternal scuff seal at the corners provides abrasion resistance forrugged environmental usage, in addition to full enclosure and sealing.Furthermore, there are no interior gussets, fillets, or doublers whichwould reduce corner space in the shelter. The entire shelter assembly isa structure where tension, bending, and shear loads are effectivelydistributed over the cross section of each panel and are transferredthrough the joints between the panels to allow full utilization of thestructural properties of the sandwich composite panels, whilemaintaining thermal insulation. Since all joints in the shelter assemblyare identical, except for variations in panel thickness, shelter panelscan be produced en masse and later be fitted together. Furthermore,since the joints are structural and suitable for assembly/disassemblycycling, it is possible to remove a shelter panel after assembly of theshelter, as described above, with convenient reinstallation of thepanel. It will be appreciated that a shelter manufactured with suchpanels and edge joint structures can be assembled in various differentsizes from modular panel sizes to provide great versatility.

This invention having been described in its preferred embodiment, andalternative embodiments also disclosed, it is clear that it issusceptible to numerous modifications and embodiments within the abilityof those skilled in the art and without the exercise of the inventivefaculty. Accordingly, the scope of this invention is defined by thescope of the following claims.

What is claimed is:

l. A structural panel consisting of:

a first, continuous outer skin;

a second, continuousdivider skin;

a third,'continuous inner skin;

a rigid foamed synthetic polymer composition material core adhesivelysecured between said first and second skins;

an uncrushed hexagonal honeycomb core positioned between said second andthird skins and attached thereto with its cells substantially normal toone of said second and third skins, so that said foamed core provideslow thermal conductivity between said first and third skins of saidpanel and said honeycomb core provides mechanical strength to saidpanel.

2. The panel of claim 1 wherein said second and third skins are ofaluminum and said honeycomb is of aluminum.

3. The panel of claim 2 wherein said aluminum second and third skins areadhesively attached to said aluminum honeycomb.

4. The panel of claim 1 wherein said foamed core has first and secondfaces respectively facing said first and second skins, said foamed corehaving grooves therein, said adhesive securing said first and secondskins to said foamed core entering into said grooves in said faces toincrease attachment strength of said first and second skins to saidfoamed core.

5. The panel of claim 3 wherein said foamed core has first and secondfaces respectively facing said first and second skins, said foam corehaving grooves therein, said adhesive securing said first and secondskins to said foamed core entering into said grooves in said faces toincrease attachment strength of said first and second skins to saidfoamed core.

1. A STRUCTURAL PANEL CONSISTING OF: A FIRST, CONTINOUS OUTER SKIN; ASECOND, CONTINOUS DIVIDER SKIN; A THIRD CONTINOUS INNER SKIN; A RIGIDFOAMED SYNTHETIC POLYMER COMPOSITION MATERIAL CORE ADHESIVELY SECUREDBETWEEN SAID FIRST AND SECOND SKINS; AN UNCRUSHED HEXAGONAL HONEYCOMBCORE POSITIONED BETWEEN SAID SECOND AND THIRD SKINS AND ATTACHED THERETOWITH ITS CELLS SUBSTANTIALLY NORMAL TO ONE OF SAID SECOND AND THIRDSKINS, SO THAT SAID FOAMED CORE PROVIDES LOW THERMAL CONDUCTIVITYBETWEEN SAID FIRST AND THIRD SKINS OF SAID PANEL AND SAID HONEYCOMB COREPROVIDES MECHANICAL STRENGTH TO SAID PANEL.
 2. The panel of claim 1wherein said second and third skins are of aluminum and said honeycombis of aluminum.
 3. The panel of claim 2 wherein said aluminum second andthird skins are adhesively attached to said aluminum honeycomb.
 4. Thepanel of claim 1 wherein said foamed core has first and second facesrespectively facing said first and second skins, said foamed core havinggrooves therein, said adhesive securing said first and second skins tosaid foamed core entering into said grooves in said faces to increaseattachment strength of said first and second skins to said foamed core.5. The panel of claim 3 wherein said foamed core has first and secondfaces respectively facing said first and second skins, said foam corehaving grOoves therein, said adhesive securing said first and secondskins to said foamed core entering into said grooves in said faces toincrease attachment strength of said first and second skins to saidfoamed core.